The present invention is directed to a printing form having a plurality of substantially planar functional zones.
From the related art in the field of planographic printing, in particular offset printing, printing plates, printing belts, printing sleeves and surfaces of printing devices, such as printing cylinders (generally referred to in the following as printing forms) are known, which, following a (re-)imaging process, carry image information and transfer an applied printing ink in accordance with the image information to a medium, such as paper.
Printing forms of this kind frequently have a layered structure, i.e., different layers are superimposed one over the other on a substrate, it being possible to assign special functions, such as absorption or reflection of radiation, and thermal insulation, to these layers.
Typically, the imaging operation includes radiating energy over the full surface or in a controlled manner in accordance with the image information, lasers often being used. In the process, the printing form is heated by the radiated energy, at least on an image dot basis, to the point where its surface temperature locally exceeds a specific transition temperature and a surface chemical or surface physical process takes place, which leads to a change in its affinity to water (or ink). In this manner, the surface of the printing form can be patterned into hydrophilic and hydrophobic (or oleophobic and oleophilic) regions.
From the European Patent Application EP 1 245 385 A2, an imageable wet-offset printing form is known, which has a layered structure. The printing form, i.e., its photocatalytically and thermally modifiable material, for example TiO2, is photocatalytically hydrophilized over the full surface area by ultraviolet radiation and thermally hydrophobized on an image dot basis by infrared radiation, the thermal energy being absorbed by absorption centers in the modifiable material or in an absorption layer underneath this material.
A first embodiment includes a 1 to 30 micrometer thick top layer of TiO2, in which absorption centers (e.g., nanoparticles of a semiconductor material) are dispersed in a fine, uniform distribution, and a sublayer of a material having good thermal conduction and a high thermal capacity for preventing too much heat from diffusing in the lateral direction.
A second embodiment includes an only 0.5 to 5 micrometer thick top layer of TiO2 and a 1 to 5 micrometer thick absorption layer disposed underneath it, from where the absorbed thermal energy can flow back into the top layer.
In both exemplary embodiments, the two layers can be superimposed on a substrate, for example of aluminum, an additional 1 to 30 micrometer thick insulating layer being able to reduce the thermal conduction to the substrate.
U.S. Pat. No. 5,632,204 also describes an imageable offset printing form, which has a polymer surface, a less than 25 nanometer thick, underlying thin metal layer, for example of titanium, for absorbing infrared radiation, and a thermally non-dissipative substrate having pigments that reflect infrared radiation. To image the printing form, it is exposed to infrared laser radiation, which penetrates into the two top layers and is reflected at the substrate back into the metal layer. The thin metal layer can additionally be provided with an antireflection coating, for example of a metal oxide, for the infrared radiation.
In addition, the U.S. Pat. No. 6,073,559 discusses an infrared-imageable offset printing form having a 10 to 500 nanometer thick hydrophilic layer of a metal-nonmetal mixture, a 5 to 500 nanometer thick metal layer, for example of titanium, for absorbing the input infrared radiation, which forms an oxide at its surface, an oleophilic, hard ceramic layer as a thermal insulator, and a substrate. At the surface of the ceramic layer, the incident radiation is reflected back into the metal layer.
Moreover, German Application DE 101 38 772 A1 discusses a rewritable printing form for printing processes using meltable printing ink. The printing form has an external layer which functions as an absorption layer, for example a 0.5 to 5 micrometer thick titanium layer, and an inner layer which functions as an insulation layer, for example a 10 to 100 micrometer thick glass or ceramic layer. Both layers are accommodated on a substrate. The absorption layer has a low thermal capacity and density and, in addition, the insulation layer has a low thermal conductivity.
Another printing form constitutes the subject matter of the still unpublished German DE 102 27 054. This reusable printing form has a metal oxide surface, for example a titanium oxide surface, which is treated with an amphiphilic organic compound whose polar region has an acidic character. By selectively inputting energy on a dot-by-dot basis, for example by infrared irradiation, an image can be produced on the printing form, and, by inputting energy over a large surface area, for example by ultraviolet irradiation, the image can be erased again.
Finally, the subject matter of the still unpublished German DE 103 54 341 is a method for patterning a printing form surface which has a hydrophilizable polymer, by inputting energy, for example by laser radiation, into one region of the printing form surface in which the polymer is hydrophilized, the printing form surface being liquefied and intermixed.
In all of the known printing forms and applied imaging methods, only one portion of the radiated energy is available for the actual imaging process. Another portion of the radiated energy dissipates, unused, due to reflection at the surface or at boundary surfaces between adjacent surfaces and due to transfer by thermal conduction into deeper-lying layers, in particular into the substrate material.
For this reason, a low-power imaging operation, in particular using multi-channel imaging systems, is problematic. To overcome the problem, the related art provides, for example, for using higher power while working with few imaging channels, and a lower imaging speed.
In addition, in the known printing forms, the imaging energy is introduced into an absorption layer from where the energy flows into a layer to be imaged, where it initiates the imaging process. In this context, the energy absorption of the absorption layer is limited by a layer temperature at which damage or destruction to the layer could occur.
For this second reason, however, it is also not possible to select an arbitrarily high power for the imaging system.